368 



Fishery Bulletin 97(2), 1999 



100 cm. Our data support the hypotheses that the 

 maximum size in greater amberjack is sex related. 

 Similar results were reported for other pelagic spe- 

 cies (Atlantic and Pacific blue marlin, and swordfish) 

 suggesting that females either grow faster, live 

 longer, or both (Wilson, 1984; Wilson et al., 1991). 



Charterboat-caught greater amberjack were col- 

 lected year-found from the Louisiana coast, provid- 

 ing us with the opportunities to examine seasonal 

 changes in the population. Size-frequency analysis 

 of these data showed that fish were largest from May 

 to September and smallest from November to Feb- 



Estimated age (yr) 



Figure 6 



Plot of the estimated age and length of north-central Gulf of Mexico 

 greater amberjack and the resultant von Bertalanffy relationship. 



ruary, suggesting a seasonal shift in the size fre- 

 quency of individuals in the population off Louisi- 

 ana. Although this seasonal size difference could be 

 due to sampling bias, we believe that greater amber- 

 jack have an affinity for warmer waters and that the 

 cooler waters associated with winter initiate an emi- 

 gration from Louisiana waters. Burch ( 1979 ) reported 

 greater ambeijack migrating southward from Decem- 

 ber to May and northward from June to December 

 in Florida. Baxter (1960) reported a northward mi- 

 gi'ation of California yellowtail (as Seriola dorsalis) 

 off California waters during early spring. The size 

 at which greater amberjack begin to mi- 

 grate is not known (Burch, 1979). 



Females tended to be more abundant 

 than males throughout our study, although 

 the female-to-male ratio varied with time 

 of year and source. This is contrary to 

 Burch ( 1979) who reported female-to-male 

 ratios from 0.6:1 to 2:1 with males more 

 numerous in all months except July, Au- 

 gust, and September Humphreys (1986) 

 reported a female-to-male ratio of 0.9:1. In 

 our study, no trend in sex ratio was de- 

 tected for charterboat-caught greater am- 

 berjack, and the overall ratio was 2.5:1. It 

 is possible that males are more abundant 

 off the west coast of Florida and females 

 are more abundant off Louisiana. Thomp- 

 son et al.^ found that male cobia iRachy- 

 centron canadum) dominated in the west- 

 central Gulf of Mexico, whereas females 

 dominated in the east-central Gulf of Mexico. 



20 40 60 80 100 



Predicted values (cm) 



120 



140 



160 



Figure 7 



Predicted versus ob.served recapture lengths of tagged greater amber- 

 jack. Predicted values were calculated by using our von Bertalanffy 

 growth parameters. The solid line covers points where the predicted 

 and observed values are equal. 



Otoliths 



Greater amberjack otoliths are small, frag- 

 ile, and complex in shape. In a compari- 

 son of external and internal features with 

 those of other pelagic species, sagittae were 

 found to be similar in shape to those of red 

 steenbras (Petriis rupestris) (Smale and 

 Punt, 1991), tunas (C.A. Wilson, unpubl. 

 data), billfishes (Wilson et al., 1991), and 

 several other carangids (Alectis, Caranx, 

 Chloroscommbrus, Elegatis, and Uraspis, 

 senior author, unpubl. data) 



We tried several models (power function, 

 logistic equation, Gompertz and Richards 

 models) to describe the relationship be- 

 tween fish size (fork length) and otolith 

 size (sagittal weight). A negative exponen- 

 tial in the form of the von Bertalanffy equa- 

 tion provided the best fit (r^=0.96) and in- 

 dicated that sagittal weight continues to 



